chore: update dotnet version in test pipeline

Author: hazzik

.github/workflows/test.yml

@@ -27,7 +27,7 @@ jobs:
     - name: Setup .NET
       uses: actions/setup-dotnet@v4
       with:
-        dotnet-version: 8.0.x
+        dotnet-version: 9.x
 
     - name: Restore
       run: dotnet restore src